1. Field of the Invention
This invention relates to electrical switches. More particularly, the invention relates to high speed electrical switches, the contacts of which have a tendency to bounce. The invention is described with respect to a mercury-wetted sealed contact switch as an illustrative embodiment of the invention.
2. Discussion of the Prior Art
Mercury-wetted sealed contact switches are in most instances not subject to contact bounce. A thin layer of mercury which wets their contact surfaces is sufficient to serve as a damper to the tendency of the contacts to bounce. However, in some switches including those which respond at frequencies close to the natural frequencies of their armatures, contact bounce can occur. U.S. Pat. No. 2,406,036 to Pollard, Jr. refers to the problem of contact bounce in relationship to a sealed contact device having a resiliently bouncing armature. The patent discloses a solution wherein a wetted mercury brake controls the movement of the armature.
The Pollard, Jr. patent disclosure relates to a slip joint in a wick transporting mercury from a pool at the bottom of the switch to its contacts in the upper portion of the switch. The joint is formed by two closely spaced parallel discs. The planes in which the discs lie are oriented substantially parallel to the direction in which the armature extends. The distance at which the discs are located from an apparent center of rotation of the armature is chosen to lie between the center and the contacts as a compromise to give high damping of the harmonic vibration and low damping of the functional operation.
The damping occurs when a resilient bending motion of the armature causes a pumping action on a quantity of mercury filling the space between the discs by capillary attraction. With one of the discs being mounted directly to the armature, the motion of the armature becomes damped. However, the disc and its supporting structure increases the mass and consequently the inertia of the armature.
A copending application, Ser. No. 793,123, filed on May 2, 1977, in the Patent and Trademark Office in the name of Asbell et al., discloses subject matter which is applicable to miniature mercury-wetted sealed contact switches. Because of a low mass of an armature in a miniature switch in comparison to larger switches, such a miniature switch is capable of quickly opening or closing in response to a command. Consequently, a substantial increase in the inertia of the armature of such a miniature switch could easily destroy a fast response time as an advantageous operating characteristic of the switch. It is therefore desirable to provide a damping structure for a switch armature which does not significantly affect the response time of the damped switch armature.
Also, a brake which damps harmonic vibrations of an armature tends to interfere with the functional motion of the armature operating close to its natural frequency. It is therefore desirable to provide an effective arrangement for neutralizing stored energy of the armature. This energy would otherwise tend to cause contact bounce.